High pressure synthesis is widely used for producing industrial diamonds. It is known that an industrial diamond containing boron can be synthesized by adding boron into a catalytic metal or the like when the diamond is produced by high pressure synthesis. It is also known that a boron atom substitutes for a carbon atom to make an acceptor level in the upper part of a valence band, i.e., at 0.37 eV, thereby making a p-type semiconductor.
Recently, diamonds containing boron, because of their above-described semiconductor characteristics, have been considered for use in various electrodes, chemical resistance sensors, conductive grinding stones, etc.,. These possible new areas of use have resulted in an increased demand for semiconductor diamonds containing boron The increased demand for semiconductor diamonds containing boron requires that the diamonds be synthesized with high efficiency and at a high yield.
In a conventional high pressure synthesis method, for example, in a method disclosed in Japanese Patent Publication No. 59-6808, boron is added together with aluminum into a catalyst metal that acts as a catalyst during diamond synthesis. The metal is employed catalytically, in molten form, to make a diamond single crystal grow on a diamond seed crystal. The quantity of boron added in the catalyst is controlled as best as possible, thereby, to the extant possible, controlling the boron content in the synthesized diamond.
In the above-described method it is difficult to control the quantity of boron added in the molten metal catalyst. In addition, it is difficult to uniformly distribute boron in the resultant diamond. Finally, diamond yields are not high.
Because of the many drawbacks in the above-described representative process, an object of the present invention is to provide purified graphite material inventive embodiments, for synthesizing semiconductor diamonds. The purified graphite material inventive embodiments, ideally, allow the production of boron or boron compound containing semiconductor diamonds inventive embodiments to be achieved at high yield. The purified graphite material inventive embodiments also allow the boron or a boron compound to be contained in the diamond inventive embodiments at a high percentage, and allow a uniform distribution of the boron or boron compound in the diamonds.